Goniometers rotate an object about an axis in space located outside the body of the unit (usually-above the platform), so the axis is not obscured by the unit itself. Goniometers have small travel range and greater stability, compared to rotation stages. Goniometers have to have different heights of points of rotation, so that, when you stack goniometers one on top of the other, they rotate an object about a common point in space (8MG00-50 on top of 8MG00-80). The mechanism rolls smoothly on ball bearings. The position is read within one revolution on the scale engraved on the dial knob sitting on the axle of the motor. Position can be read to each step. Overall position accounting is up-to your computer. Goniometers have two limit switched to signal an "out of limits" error situation. The switches may also be used to roughly establish a zero reference. The stage is driven by stepping motor. A dial knob on its axle allows manual drive.